In multi-disk shifting elements wobbling of the disks is a well known problem, which is exacerbated at large speed differences between the outer and the lining disks in the open condition of the shifting element, such that with shifting elements of large diameter with high circumferential speeds, the outer disks in particular tend to wobble. This involves nutation and precession movements of individual disks, which with increasing speed lead to periodic, axial oscillations of the disk packet as a whole. Disadvantageously, disk wobble leads to high drag torques and results in a temperature increase. With quantitatively small idling torques disk wobble can also result in very large torque losses since some disks, due to their wobbling motion, produce greater friction against the surrounding medium and/or against adjacent disks; furthermore, disk wobble can lead to damage or even destruction of the multi-disk shifting element.
Moreover, sticking of the lining disks to the outer disks of the shifting element in the open condition can also result in higher drag torques and temperature elevation.
To prevent disk wobble and sticking of the lining disks to the outer disks, it is known from the prior art to make the outer disks with corrugations. The corrugations damp or prevent disk wobble; furthermore, the corrugations separate disks that tend to stick to one another.
For example, from U.S. Pat. No. 7,806,245 B2 a clutch system is known, which comprises a rotation axis rotated by a torque, at least one pressure plate arranged in an outer area of the rotation axis and which can move along an axial direction of the rotation axis, at least one disk arranged in alternation with the pressure plate and which can move along an axial direction of the rotation axis, and a piston which applies a force on the disk in the axial direction of the rotation axis, so that a frictional force is produced between the pressure plate and the disk. In this case each disk has at least one bend or corrugation along its radial direction; another multi-disk clutch with disks having corrugations in the same direction as one another is described in U.S. Pat. No. 2,927,673 A.
Furthermore, U.S. Pat. No. 1,340,885 A describes a multi-disk clutch with disks corrugated in the same direction and disks corrugated in opposite directions.
Corrugations of the outer disks can be regarded as a geometrical defect which, in combination with the rotating lining disks, leads to oscillations of the system which, by virtue of the corresponding torque transfer via the drive-train, are perceptible during shifting processes. A design of a multi-disk shifting element with disks having oppositely directed corrugations reduces the oscillations during shifting processes but increases the elasticity of the disk packet as a whole, which disadvantageously leads to problems in the control of the shifting processes that make themselves noticeable in the form of perceptible torque impulses.